Before we discuss about what is a mate and what is a soul mate, let me ask you one simple question. Do you have a passion in life- anything that you love doing and enjoy? If yes, does your love partner share that interest? What if he/she does not? Let us talk about that.
After sometime the physical attraction will reduce. The romantic feelings will get battered with time, but your passion for what you enjoy doing will not reduce. If your partner shares the same passion, you will enjoy doing that together, otherwise, you will look for mates with whom you can share your passion and slowly drift away from your partner.
This is not uncommon. Look at most of the wealthy people. Their main passion is to make money and become more powerful. The process of making money thrills them. What of their partners? That is why you will find marriages getting broken rapidly with such groups. Before you decide on a partner, try and get one who shares your passion and who can be your soul mate in true sense. Your relationship will survive much longer.